Device with flexible multilayer system for contacting or electrostimulation of living tissue cells or nerves

ABSTRACT

The object,—to create a printed circuit board for an implant having improved properties in connection with the electrical contacting via the contact points of the conductor tracks on the printed circuit board,—is achieved, according to the present invention, by means of a device for contacting and/or electrostimulation of living tissue cells or nerves with having a printed circuit board having with at least one contact point for electrical contacting, the printed circuit board encompassing comprising a flexible multilayer system with at least one conductor track. In accordance with the invention, the contact points for the conductor track in the multilayer system are galvanically reinforced. To this end, a galvanically reinforced layer is grown onto the already preprocessed contact point, for example by means of a galvanic process. By virtue of the application of one or more additional material layers onto the contact points of the conductor tracks, these latter are mechanically more stably anchored in the printed circuit board in mechanically more stable manner and hence become more reliable in their function.

This application is the U.S. National Stage of PCT/EP 2007/000685, filedon Jan. 26, 2007, which claims priority to DE 10 2006 008 050.5, filedon Feb. 21, 2006, both of which are incorporated herein by reference intheir entirety.

The present invention relates generally to systems that serve forcontacting living tissue or nerves. The invention relates to a devicefor contacting or electrostimulation of living tissue cells or nerveswith a printed circuit board encompassing at least one contact point forelectrical contacting of implants with multilayer systems with printedcircuit boards in which at least one contact pad of a flexible printedcircuit board is positively anchored in the printed circuit board,wherein a mechanical reinforcement of the contact pad being is achievedby galvanic growth of conductor-track material.

Devices are known in the form of implants for stimulating living tissue,such as, for example, implants for the retina of the human eye or forthe human inner ear. As a rule, such implants encompass a number ofstimulating electrodes, via which electrical stimulating pulses aredelivered to the surrounding tissue or to the cells, in order in thisway to stimulate the nerves and hence thereby to re-establish or toimprove their function thereof.

Known implants are frequently an integral part of systems that encompasselectrical or electronic components for diagnostic purposes such as, forexample, the electrical measurement of bodily functions, blood pressure,blood sugar or temperature. Such systems may also include glucosesensorics, ultrasound sensorics, components for image-recording or forsound-recording and, in particular, components for actoric purposes.With such systems it may also be a question of stimulation systems thatinclude componentsfor actoric purposes such as, for example, forelectrostimulation, defibrillation, emission of sound or emission ofultrasound. As a rule, such systems encompass comprise a substrate inthe form of a printed circuit board on which the electronic modulescomponents are arranged, with electrical contacts that are in direct orindirect contact with the body tissue such as, for example, nerve tissueand muscle tissue, or with body fluids such as blood, for example,blood.

In order to keep the dimensions of the electrical or electroniccomponents as small as possible, besides ceramic substrates, flexibleprinted printed circuit boards made of plastics,—for example, polyimide,parylenes,—are also being increasingly employed. Such flexible printedprinted circuit boards can are able to be structured in very finedimensions with a layer thickness of the conductor track from a fewnanometres up to a few hundred nanometres and with a conductor-trackwidth of, for example, a few micrometres with the aid of establishedprocesses for producing microchips having very fine dimensions with alayer thickness of the conductor track from a few nanometres up to a fewhundred nanometres and with a conductor-track width of, for example, afew micrometres.

As a rule, such a flexible printed circuit board consists of one or moreinsulating layers, for example made of polyimide, parylenes or otherplastics, insulators or flexible semiconductors, on which conductortracks, contact areas or, where appropriate, through-connectionsmetallised holes between several multiple conductor-track planes haveare been established. For the electrical contacting of the conductortracks, corresponding contact points or contact pads are provided, viawhich electrical leads and/or modules can, for example, can be attached,in order to connect the electronic components on the printed circuitboard to external components of the stimulation system.

With these flexible printed circuit boards, however, there exists theproblem that the thin conductor tracks are mechanically extremelysensitive, particularly at their contact points, which can result inloss of the electrical contact with the contact points and the conductortracks. A further problem of these contact points or contact padsconsists in the anchorage within the very thin, flexible printed circuitboard for the implant. As a rule, the conductor track has a thicknessfrom a few nanometres up to a few hundred nanometres, and the insulatinglayer has a thickness of a few micrometres. Critical in this regard isthe fact that the contact point is only insufficiently anchoredmechanically in the conductor track. In particular, as a result ofmechanical loads in the course of the manufacturing, inserting ofcomponents assembly, or processing of the printed circuit boards for animplant, a contact pad can be easily dissolved loosened out of from theflexible printed circuit board by reason of mechanical compressiveforce, tensile force, shear force, flexural stress, expansion, vibrationby ultrasound etc.

It is therefore an object of the present invention to create a printedcircuit board for an implant having improved properties in connectionwith the electrical contacting via the contact points of the conductortracks on the printed circuit board.

This object is achieved by means of the device according to theinvention having the features according to claim 1. Advantageous furtherdevelopments of the invention are specified in each of the dependentclaims.

According to one aspect of the present invention, the aforementionedobject is achieved by means of a device for contacting and/orelectrostimulation of living tissue cells or nerves with a printedcircuit board that encompasses at least one electrically insulatingmaterial layer on which a conductor-track layer with at least oneconductor track is arranged. For the electrical contacting of theconductor track, at least one contact point is provided. Above theconductor track at least one additional material layer is arranged,through which the contact point extends. In this way, the conductortrack is electrically contactable from outside of the printed circuitboard through the additional material layer via the contact point.

According to a further aspect of the present invention, theaforementioned object is achieved by means of a process method forproducing a printed circuit board in the form of a multilayer system fora device for contacting and/or electrostimulation of living tissue cellsor nerves, said process comprising the following steps:

-   -   generating a first insulating material layer,    -   generating a conductor track on the first insulating material        layer,    -   generating a second insulating material layer,    -   generating at least one window in the second insulating material        layer,    -   filling the window in the second insulating material layer with        an electrically conducting material for to the purpose of        generating a contact point that exhibits an electrical contact        with the conductor track    -   generating an additional insulating material layer on the second        insulating material layer,    -   generating at least one window in the additional insulating        material layer, the window in the additional insulating material        layer exhibiting smaller lateral dimensions than the window in        the second insulating material layer,

filling the window in the additional insulating material layer with anelectrically conducting material for to the purpose of generating acontact pad that exhibits an electrical contact with the contact point.

Consequently, with the process method according to the invention thecontact points for the conductor tracks of the implant,--such as, forexample, a stimulating electrode,--are reinforced by means of one ormore additional material layers. In this connection, a galvanicallyreinforced layer is grown onto the already preprocessed contact point,for example by means of a galvanic process. Alternatively, besides thegalvanic application of metal, other suitable processes for applying oneor more material layers may also be employed, such as sputtering, forexample. Through the subsequent application of one or more additionalmaterial layers onto the prestructured contact points of the conductortracks, these latter are mechanically more stably integrated within theprinted circuit board in a mechanically more stable manner and hencebecome more reliable in their function,--i.e. the contact points can becontacted more reliably, and the electrical contact better can bemaintained better, and the contact points are anchored better in thestimulating electrode.

According to a preferred embodiment of the present invention, theflexible printed circuit board for an implant consists of multiplelayers of an insulating material with conductor tracks, arrangedin-between, said layers, or underneath, them, or on top of them, whichconductor tracks are mechanically reinforced prior to the application offurther surface layers of insulating material in the region of thecontact points prior to the application of further surface layers ofinsulating material. The application of one or more mechanicallyreinforcing layers on the printed circuit board is effected, forexample, by means of galvanic processes, by means of sputtering or byother suitable processes. Alternatively, or in addition, appropriatecontact pads made of metal may are also able to be fastened to thecontact points. This is preferably done by gluing them on with the aidof a conductive adhesive, by soldering, welding, ultrasonic bonding,thermocompression bonding, crimping pressing on or clipping.

The manufacture of the fine structures of a flexible printed circuitboard that is suitable for use in an implant is carried out, as a rule,with the aid of lithographic processes that are already established forthe production of semiconductors from silicon wafers.

With this process method, it is possible for galvanically reinforced andpositively anchored contact pads to be generated with positive anchoragein flexible printed circuit boards, which can be used in devices with aflexible multilayer system for contacting or electrostimulation ofliving tissue cells or nerves. The contact pads may be fitted optionallyon the upper side and/or on the underside of the printed circuit boardof the flexible multilayer system. Instead of, or together with, thecontact pads, electrodes for electrostimulation of living tissue ornerves can also be established or arranged in the flexible printedcircuit board. Via through-metallised holes connections through theinsulating material layers of the flexible printed circuit board, it ispossible for electrical contacts from the contact pads or from thecontact points to the inner metal conductor tracks of the multilayersystem are able to be produced.

A further special feature of the process method for producing a printedcircuit board according to the present invention that is suitable foruse in an implant consists in the fact that, on the one hand, a galvanicmanufacturing process is employed in order to achieve mechanicalreinforcements of the contact pads or at the contact points, and thatthese galvanically reinforced contact points are positively anchored inthe printed circuit board by means of internal electroplating layers;this means that the internal inner electroplating layer of the contactpad in question is larger in its lateral dimensions than the externalouter electroplating layer of the contact pad, so that a good mechanicalanchorage is obtained in relation to mechanical forces acting fromoutside. This good mechanical anchorage of the contact pad(s) in theprinted circuit board is an important prerequisite for mechanicalinterconnection techniques to be carried out subsequently, such as, forexample, ultrasonic bonding, conductive bonding, thermocompressionbonding, flip-chip bonding and other electrical interconnectionprocesses.

A good mechanical anchorage of the contact pad in the printed circuitboard for an implant is also a prerequisite for the production ofmechanically robust electrodes on the flexible printed circuit board,this being which is of great importance in neuroprosthetics, forexample. Such electrodes can be used, in particular, forelectrostimulatory purposes, for example in a retinal implant, in acochlear implant, for brain-stem stimulators, deep-brain stimulations,spinal-cord stimulators or other stimulators. On the other hand, thereis also the possibility also exists of realising bleeder recordingelectrodes with the described process method, which may, which, forexample, can be used for electrophysiological measurements of neuralactivity or of the impedance of biological or chemical systems.

Further particulars, preferred embodiments and advantages of the presentinvention will become apparent from the following description withreference to the appended drawings. Shown are:

FIG. 1 illustrates a schematic representation of the structure of aprinted circuit board according to a first preferred embodiment of thepresent invention for use in a device for contacting orelectrostimulation of living tissue cells or nerves;

FIG. 2 a illustrates a schematic representation of the structure of aprinted circuit board according to a second preferred embodiment of thepresent invention for use in a device for contacting orelectrostimulation of living tissue cells or nerves;

FIG. 2 b illustrates a schematic sectional representation of theembodiment of the printed circuit board according to the invention thatis shown in FIG. 2 a.

FIG. 3 a illustrates a schematic representation of the structure of aprinted circuit board according to a third preferred embodiment of thepresent invention for use in a device for contacting orelectrostimulation of living tissue cells or nerves; and

FIG. 3 b illustrates a schematic sectional representation of theembodiment of the printed circuit board according to the invention thatis shown in FIG. 3 a.

FIG. 1 is a schematic representation of the structure of a printedcircuit board L according to a first preferred embodiment of the presentinvention for use in a device for contacting or electrostimulation ofliving tissue cells or nerves.

The printed circuit board L represented in FIG. 1 encompasses comprisesthree material layers 1, 2, 3 made of an electrically insulatingmaterial such as, for example, polyimide, parylenes or anotherinsulator. On these insulating layers 1, 2, 3 a lower conductor track 4and an upper conductor track 5 are formed. The conductor tracks 4 and 5are each situated lie in a corresponding conductor-track plane, wherebythe conductor-track plane of conductor track 4 being is located betweenthe insulating material layer 1 and the insulating material layer 2, andthe conductor-track plane of conductor track 5 being lies situatedbetween the insulating material layer 2 and the insulating materiallayer 3. In the case of the embodiment of the printed circuit board Laccording to the invention that is represented in FIG. 1, the conductortracks 4 and 5 are electrically connected to one another via athrough-metallised hole connection 6 between the conductor-track planes.

The upper conductor track 5 is furthermore provided with a contact areaand/or a contact point 7 which extends from the conductor-track plane ofthe upper conductor track 5 as far as to the outer edge of the printedcircuit board L. For the electrical contacting of the conductor tracks,contact points 7 are provided, to which external electrical leads can beattached in order to connect the electronic components on the printedcircuit board L to with further electrical components of a system. Anelectrode 8 may also be applied onto the contact point 7. The conductortracks 4, 5 may be constructed, for example, from titanium, copper,gold, silver, platinum, conductive plastic or other electricallyconductive materials. The printed circuit board L according to theinvention can be produced by processes for generating microstructuressuch as are known, for example, from the production of semiconductormodules. With the aid of such processes, very fine dimensions of theprinted circuit board L can be achieved, whereby the layer thickness ofthe conductor tracks 4, 5 may amount to from a few nanometres up to afew hundred nanometres and the layer thickness of the insulatingmaterial layers 1, 2, 3 may amount to a few micrometres.

In order to achieve the aforementioned object of a mechanically morestable and functionally more reliable arrangement of the contact points7 or electrode pads 8 in the printed circuit board L, according to thepresent invention the contact points 7 for the conductor tracks 5 aresubsequently reinforced by means of one or more additional materiallayers 9. In the case of the first embodiment of the printed circuitboard L according to the invention that is represented in FIG. 1, alayer 9 made of electrically insulating material is arranged on thecontact point 7 of the printed circuit board L. Through the arrangementof one or more additional material layers 9 on the contact point 7 ofthe conductor track 5, the contact point 7 is mechanically more stablyanchored in the printed circuit board L in a mechanically more stablemanner and hence can be contacted more reliably.

Arranged on the contact point 7 is a contact pad 8 made of anelectrically conductive material which extends through the additionalmaterial layer 9, via which pad the contact point 7 can be contactedfrom outside. This is preferably done by sputtering, galvanic growth,gluing on with the aid of a conductive adhesive, by soldering, welding,ultrasonic bonding, thermocompression bonding, crimping pressing orclipping. Several Multiple additional material layers 9 may also bearranged on the material layer 3 above the conductor-track plane withthe upper conductor track 5. The contact pad 8 made of electricallyconducting material is then formed in such a way that it extends fromthe contact point 7 through all the additional material layers 9, inorder to be able to contact the contact point 7 electrically fromoutside of the conductor tracks. In this way, galvanically reinforcedand positively anchored contact pads 8 or even electrodes can beestablished both on the upper side and on the underside of the printedcircuit board L, which via respective contact points 7 enable anelectrical contact with the inner metallic conductor tracks 4 and 5 ofthe printed circuit board L.

FIG. 2 a shows a schematic representation of the structure of a printedcircuit board L according to a second preferred embodiment of thepresent invention with a contact point 7, and contact pad 8 formed onthe upper side of the printed circuit board L, and FIG. 2 b shows aschematic sectional representation of the embodiment of the printedcircuit board L according to the invention that is shown in FIG. 2 a.The embodiment of a printed circuit board L according to the inventionthat is shown therein again encompasses comprises three insulatingmaterial layers 2, 3 and 9, as well as two conductor-track layers withelectrically conducting conductor tracks 4 and 10. The lower conductortrack 4 is situated between the insulating material layers 2 and 3,whereas the upper conductor track 10 is arranged between the insulatingmaterial layers 3 and 9.

The lower conductor track 4 is electrically contacted via athrough-metallised hole connection 6, and the lower conductor track 4 isequipped with a contact point 7 on which a contact pad or electrode pad8 is arranged. Both the through-connection metallised hole 6 and as wellas the contact point 7 and the contact pad 8 are designed constructed inthe form of an electroplating layer,—i.e. they have been generated as agalvanic metallic coating by a galvanic process. Above the upperconductor track 10 an additional insulator layer 9 is arranged which issituated above the contact point 7 and includes within itselfincorporates the contact pad 8 within it. Consequently, through the useof galvanic processes a reinforcement of the contact point 7 or of thecontact pad 8 is achieved, and through the application of the additionalmaterial layer 9 on the upper conductor-track layer opposite theinsulating material layer 3 a positive anchorage of the contact point 7,8 on the upper side of the printed circuit board L is achieved.

The contact pad 8 extends from the contact point 7 as far as the upperedge, or beyond it, of the additional material layer 9, so that theconductor track 4 is electrically contactable from outside of theprinted circuit board L. As a result, the contact point 7 encompassescomprises a lower part and an upper part, whereby the lower partexhibits a larger lateral dimension than the upper part. In this way,the contact point 7, and the contact pad 8 is anchored better in theprinted circuit board L and is less sensitive to mechanical deformationsand/or tensile forces perpendicular to the flexible printed circuitboard L.

FIG. 3 a shows a schematic representation of the structure of a printedcircuit board L according to a third preferred embodiment of the presentinvention, with a contact point 7, and contact pad 8 formed on theunderside of the printed circuit board L, and FIG. 3 b shows a schematicsectional representation of the embodiment of the printed circuit boardL according to the invention that is shown in FIG. 3 a. The embodiment,shown therein, of a printed circuit board L according to the inventionhas, in part, a similar structure to that of the embodiment shown inFIGS. 2 a and 2 b.

The embodiment of a printed circuit board L according to the inventionthat is shown in FIGS. 3 a and 3 b exhibits a contact point 7, and acontact pad 8 on the underside and again encompasses comprises threeinsulating material layers 2, 3 and 9, as well as two conductor-tracklayers with electrically conducting conductor tracks 4 and 5. The upperconductor track 4 lies situated between the insulating material layers 2and 3, whereas the lower conductor track 5 is arranged between theinsulating material layers 3 and 9.

The upper conductor track 4 is electrically contacted via a contactpoint 7, and the lower conductor track 5 is electrically contacted via acontact pad 8. The contact point 7 and the contact pad 8 have again beengenerated by a galvanic process. Below the lower conductor track 5 anadditional insulating material layer 9 is arranged which lies situatedbelow the contact point 7 and encompassesloses the contact pad 8. Thecontact pad 8 extends from the contact point 7 as far as the lower edge,or beyond it, of the additional material layer 9, so that the conductortrack 4 is electrically contactable from outside of the printed circuitboard L. In this way, the contact point again consists of a first part 7which exhibits a larger lateral dimension than the second part 8 and is,as a result, reliably anchored in the printed circuit board L.

List of Reference Symbols

-   1 insulating material layer or insulator layer-   2 insulating material layer or insulator layer-   3 insulating material layer or insulator layer-   4 conductor track or conductor-track plane-   5 conductor track or conductor-track plane-   6 through-connectionmetallised hole-   7 lower part of the contact point-   8 upper part of the contact point or contact pad-   9 insulating material layer or insulator layer-   10 conductor track or conductor-track plane-   A sectional plane of the representation in FIG. 2 b-   B sectional plane of the representation in FIG. 3 b-   L printed circuit board

The invention claimed is:
 1. A device for contacting and/orelectrostimulation of living tissue cells or nerves, the devicecomprising: a flexible circuit board including at least one contactpoint, the flexible circuit board including the following layers: atleast one electrically insulating material layer and at least oneconductor-track layer having a conductor track, the at least oneelectrically insulating material layer formed over the at least oneconductor-track layer; and at least one additional insulating materiallayer, the at least one additional insulating material layer formed overthe at least one electrically insulating material layer and arranged ona portion of the contact point, the at least one additional insulatingmaterial layer configured to reinforce the contact point in the circuitboard, wherein the conductor track is electrically contactable fromoutside of the circuit board through the additional insulating materiallayer via the contact point, wherein the at least one contact pointincludes: a first part that is in direct contact with one of the atleast one conductor-track layer, and a second part that is in contactwith the at least one additional insulating material layer, wherein thefirst and second parts of the at least one contact point extend parallelto each other, wherein the first part has larger lateral dimensions thanthe second part, and wherein the second part is provided in the form ofa contact pad.
 2. The device according to claim 1, wherein the firstpart of the contact point is at least partially overlapped by theadditional material layer, and the second part of the contact point isat least partially surrounded by the additional material layer.
 3. Thedevice according to claim 1, wherein the at least one additionalinsulating material layer includes more than one additional insulatingmaterial layer, wherein the contact point extends from the conductortrack through the at least one additional insulating material layer asfar as an outer edge of the circuit board.
 4. The device according toclaim 1, wherein the conductor track is applied on one of theelectrically insulating material layers.
 5. The device according toclaim 1, wherein the conductor track is integrated within one of theelectrically insulating material layers.
 6. The device according toclaim 1, wherein the conductor track is arranged between twoelectrically insulating material layers.
 7. The device according toclaim 1, wherein the at least one conductor-track layer includes severalconductor tracks which are substantially separated from one another byat least one of the at least one insulating material layer.
 8. Thedevice according to claim 1, wherein the at least one conductor-tracklayer includes several conductor tracks which are electrically connectedto one another via through-connections or via electroplating layers. 9.The device according to claim 1, wherein the conductor-track layers arearranged parallel to one another.
 10. The device according to claim 1,wherein the thickness of the conductor-track layers lies within therange between a few nanometres up to a few hundred nanometres and thelayer thickness of the insulating material layers lies within the rangeof a few micrometres.
 11. The device according to claim 1, wherein theconductor-track layers and the insulating material layers are arrangedparallel to one another.
 12. The device according to claim 1, whereinthe contact point is configured for electrically contacting theconductor track and is arranged on the upper side and/or on theunderside of the circuit board.
 13. The device according to claim 1,wherein the contact point is configured for electrically contacting theconductor track and wherein the second part includes a contact pad orelectrode pad which is electrically contactable from outside of thecircuit board.
 14. The device according to claim 13, wherein the contactpoint or the contact pad extends at least as far as an outer edge of thecircuit board or projects beyond it.
 15. The device according to claim13, wherein the contact point and/or the contact pad is/are integratedwithin the additional material layer.
 16. A system for electricallycontacting and/or electrostimulation of living tissue or nerves via oneor more electrodes having a device according to claim
 1. 17. The deviceaccording to claim 14, wherein the contact point and/or the contact padis/are integrated within the additional material layer.
 18. The deviceaccording to claim 1, wherein the first part is disposed in or in directcontact with the at least one electrically insulating material layer.19. The device according to claim 1, wherein the first part is in directcontact with the at least one additional insulating material layer, andwherein the first part is incorporated into the at least oneelectrically insulating material layer.
 20. The device according toclaim 1, wherein the second part is formed in the at least oneadditional insulating material layer.
 21. A device for contacting and/orelectrostimulation of living tissue cells or nerves, the devicecomprising: a flexible circuit board including at least one contactpoint that includes a first part and a second part, the flexible circuitboard including the following layers: at least one electricallyinsulating material layer and at least one conductor-track layer havinga conductor track, the at least one electrically insulating materiallayer formed over the at least one conductor-track layer; and at leastone additional insulating material layer formed over the at least oneelectrically insulating material layer and the first part, the at leastone additional insulating material layer configured to reinforce thecontact point in the circuit board, wherein the conductor track iselectrically contactable from outside of the circuit board through theadditional insulating material layer via the contact point, wherein: thefirst part is in direct contact with one of the at least oneconductor-track layer, wherein the first part of the contact point is atleast partially overlapped by the additional material layer, and thesecond part is in contact with the at least one additional insulatingmaterial layer, wherein the first and second parts of the at least onecontact point extend parallel to each other, wherein the first part haslarger lateral dimensions than the second part and the second part isprovided in the form of a contact pad, wherein the second part of thecontact point is at least partially surrounded by the additionalmaterial layer.